The grim warnings issued at the height of the BSE epidemic in cattle, about thousands falling prey to vCJD, have so far failed to materialise.

But they have not yet gone away completely - and there is still a chance that cases will multiply many-fold more from those currently known to doctors.

All of which makes, say experts, the results of a groundbreaking experimental treatment on a single patient all the more important.

But now we have the first glimmer of scientific evidence that a treatment might be able to have an impact on this devastating disease.

Nineteen-year-old vCJD patient Jonathan Simms should be dead by now, according to many of his doctors.

But he has outlived all their expectations, repaying the determination shown by his father Don in seeking out probably the only drug in the world that could help him and forcing the NHS to give it to him.

It could be that people without this gene simply have a longer incubation period - so we could see many more cases

Dr Chris Pomfrett, University of Manchester

From a state in which the downward spiral towards death had already set in, he has recovered to a stable condition and put on weight.

More remarkably, there is distinct evidence that the drug pentosan polysulphate has had some kind of impact on his badly-damaged brain.

Guarded optimism

From a virtually unresponsive state, Jonathan has become far more able to interact with his family, on occasion attempting to call out for his mother Karen, and even respond to instructions to lift his arm.

Regaining the ability to swallow is probably a lifesaver - vCJD patients normally die because they develop pneumonia after saliva flows down into their lungs.

He has missed the birth of his baby sister

His medical team - and family - are intensely cautious people - and unwilling to speculate too far about the benefits of the drug, and what it might offer to others.

But their "guarded optimism", as Don Simms put it, cannot disguise the fact that it is possible that given to a vCJD patient at a much earlier stage, pentosan - or an improved version of it - might be able to deliver much, much more.

Dr Mark McClean, the family's GP, said bluntly: "If a member of my family was diagnosed with vCJD, I would want him or her to be on that drug tomorrow - and I would demand it."

The pioneering experiments on Jonathan fall far short of the standards of proof and safety normally expected in clinical trials.

Drug firm hope

Doctors attending the conference on Friday put out a demand for investment from pharmaceutical firms to organise proper testing and evaluation.

Given the choice between certain death in weeks or months, or a treatment that might not work, there's no choice - I would choose the treatment.

Dr Mark McClean, family GP

There are fears that the relatively small number of people with the disease mean that drug firm interest is likely to be limited - but Dr Chris Pomfrett, a BSE and vCJD researcher, says that this may not be the case.

He said: "What we have to remember is that everyone diagnosed with vCJD so far has had a particular genetic make-up.

"It could be that people without this gene simply have a longer incubation period - so we could see many more cases.

"In addition, many more countries are experiencing their own problems with BSE, and cases of vCJD are starting to emerge abroad. This is a worldwide disease."

Test breakthrough

Dr Pomfrett may be responsible for an equally important breakthrough - a reliable test for vCJD.

Without a test, even if a treatment were available, patients would not get it until brain damage from vCJD had already happened.

However, the Manchester University researcher says he can spot BSE in cattle a year before they fall ill - and should be able to do the same in humans, or at least provide a swift confirmation at the first sign of symptoms.

But there are major ethical concerns about having a test in isolation - it would be pointless to screen healthy members of the public for a disease, and then tell them it was terminal, with no hope of a cure.

He said: "Now there is a potential treatment, the ethical concerns about having such a test in humans are reducing - because we could actually offer these people something if they tested positive.

He said that the assistance of families of vCJD patients would now be invaluable if the test, and the treatment, were to be evaluated further.

No guarantees

The family of Jonathan Simms are prepared for the fact that they cannot rely on the drug holding off his vCJD forever.

They also do not expect pentosan to necessarily produce any further improvements, if the the dose is increased.

They are prepared to care for their severely-disabled boy as long as it takes - holding out in hope of other medical breakthroughs that could offer his brain a chance to rebuild itself.

Don Simms says he is no "evangelist" for the drug - but as news of the progress made by his son has spread, other families are rumoured to be seeking the chance to use it to treat their seriously-ill sons, daughters, wives and husbands.

It is the logic of people used to living with little or no hope.

Dr Mark McClean said: "Given the choice between certain death in weeks or months, or a treatment that might not work, there's no choice - I would choose the treatment."